Abstrak Latar belakang penelitian ini adalah rendahnya penggunaan Lembar Kegiatan Siswa (LKS) di sekolah dasar khususnya pada mata pelajaran IPA kelas IV-C SDN Kebraon II/437 Surabaya. Hal tersebut terjadi sebab guru kurang menguasai penggunaan LKS yang sebenarnya dalam pembelajaran. Tujuan dari penelitian menggunakan Lembar Kegiatan Siswa (LKS) berbasis pendekatan saintifik adalah untuk mengetahui efektivitas penggunaan LKS dalam pembelajaran, keterlaksanaan penggunaan LKS berbasis pendekatan saintifik, mengetahui hasil belajar siswa, dan kemampuan berpikir kritis siswa. Penelitian ini menggunakan model pengembangan Four-D Model yang terdiri dari empat tahap yaitu Define, Design, Develop, dan Disseminate. Namun dalam pengembangan ini hanya diterapkan tiga model yaitu define, Design, dan Develop karena menyesuaikan dengan kebutuhan dari peneliti. Pada tahap define, dilakukananalisis kondisi yang ada di lapangan yang disesuaikan dengan perumusan tujuan. Tahap design, peneliti menyusun tes, memilih format dan menyusun rancangan awal LKS. Tahap develop, rancangan LKS ditelaah oleh ahli materi, dilakukan uji validasi LKS, dilakukan uji coba terbatas pada subjek penelitian yaitu pada kelompok terbatas dan kelas sesungguhnya siswa kelas IV SDN Kebraon II/437 Surabaya, dan diperoleh produk akhir penelitian. Teknik pengumpulan data dalam penelitian ini menggunakan teknik validasi, observasi dan tes hasil belajar. Persentase aktivitas guru untuk validator 1 sebesar 90% , validator 2 sebesar 82,5% dan rata-rata dari kedua validator memperoleh 85,83%. Kelayakan LKS dari ketiga validator sebesar 92%, 96%, 80% dan rata-rata persentase kelayakan LKS sebesar 89,33%. Pada observasi pendekatan saintifik siswa dari kedua validator amsing-masing memperoleh 83,5% dan 82,61% dengan rata-rata persentase sebesar 83,03%. Dapat disimpulkan bahwa pengembangan Lembar Kegiatan Siswa (LKS) dapat meningkatkan hasil belajar siswa dan memiliki kriteri sangat valid untuk digunakan dalam proses pembelajaran. Kata Kunci: Lembar Kegiatan Siswa, Hasil Belajar, Kemampuan Berpikir Kritis Abstract The background of this study was the low rate of utilization of Student Learning Sheet in elemetary school, especially for science subject for the fourth grade in C classroom of SDN Kebraoin II/437 Surabaya. It emerged since the teacher did not comprehend how to use student learning sheet during the learning process. This study using scientific-approach-based student learning sheet was aimed to describe the effectiveness of the utilization of student learning sheet in the learning process, the establishment of implementing scientific-approach-based student learning sheet, to describe students’ learning results, and to describe students’ critical thinking ability. This research is a developmental research using Four-D Model developing model which consists of four stages; they are Define, Design, Develop, and Disseminate. Nonetheless, in this current research, only three stages were employed; they are Define, Design, dan Develop, since it is adjusted to the needs of the research. In Define Stage, field condition analysis is managed adjusted to the objectives. In Design Stage, the reseacrher created tests, selected the format and arranged the initial form of the student learning sheet. In Develop Stage, the initial forn of student learning sheet was reviewed by material expert, validation test toward student learning sheet was carried out, limited-try-out-test was administered toward the research subjects; to the group limited and the class real of the fourth graders of SDN Kebraon II/437 Surabaya, and the final research product was established. The data collection techinque uesd are validation technique, observations, and learning result tests. The percentages of teacher’s activity for validator 1 and validator 2 are 90% and 82.5%, respectively; while the mean score of both validators is 85.83%. The appropriateness rate of those three validators reach out 92%, 96%, and 80%, respectively; while the mean score of appropriateness rate reaches out 89.33%. Based on the observations, students’ scientific approach from both validators reach out 83.5% and 82.61%, respectively; while the mean score is 83.03%. It can be concluded that the developing of student learning sheet can improve students’ learning result and it is considered highly valid to be used during learning process Key Terms:Student Learning Sheet, Learning Result, critical thinking ability